The bearing surfaces of the tibia and femur of the knee joint are vulnerable to stress, arthritic and other disease induced deterioration and it has become common practise to replace these bearing surfaces with prosthetic devices. These devices generally fall into three main types ranging from the relatively primitive hinge-type prosthesis to a somewhat more sophisticated ball and socket-type prosthesis to the now preferred, unconstrained rolling and sliding surface-type prosthesis in which the tibial and femoral components are unconnected. Typical of the hinge-type prosthesis is that shown by Lacey in U.S. Pat. No. 4,262,368 issued Apr. 21, 1981. An example of the ball and socket-type prosthesis is shown by Averill et al in U.S. Pat. No. 3,728,742 issued Apr. 24, 1973 and an example of the rolling surface-type is shown by Waugh et al in U.S. Pat. No. 3,869,731 issued Mar. 11, 1975. Attention is also directed to U.S. Pat. Nos. 3,816,855, 4,052,753, 4,404,691 and 4,224,696 which show various alternative forms of knee joint prostheses. The prior art has, however, paid scant attention to optimizing the design of the tibial component. Generally the tibial component has simplistically been considered as a substantially flat, symetrical plate against which the femoral component articulates, and this approach results in relatively poor life of the prosthesis, loosening of the tibial component due to bone necrosis beneath the prosthesis. The initial rigid fixation necessary for biological bone ingrowth is difficult to achieve because the epiphyseal shell is largely unrestrained in current prostheses, thus resulting in high shearloading during load-bearing. This, in turn, leads to micromovement loosening of the prosthesis and premature failure of originally good interfaces particularly when the prosthesis migrates, causing sinking of the medial side. This is compounded by the varus malalignment that is produced.